496 BUTTER DEFECTS 



brought about in pure butter fat and other fats which do not 

 contain bacterial life, by enzymic action in the presence of mois- 

 ture. Air, light and heat, and the presence of catalizers, such as 

 acids and alkalies, favor the development of rancidity. 



In the case of butter, however, it is conceded by the best 

 authorities that bacteria and molds are the chief factors that 

 hydrolize the fats, making the butter rancid. Jensen 1 and Kirch- 

 ner 2 demonstrated that certain species of micro-organisms, very 

 commonly present in butter, are capable of hydrolizing the fat 

 in butter to a very marked degree and of producing butter with 

 an intense rancid odor and flavor. The chief of these organisms 

 are Oidium lactis, Cladosporium butyri, Bacillus fluorescence 

 liquefaciens and Bacillus prodigiosus. Lewkowitsch 3 suggests 

 the possibility that even in the case of rancidity produced by 

 these micro-organisms, the hydrolysis may be due to enzymes 

 produced by them rather than by their direct action on the fat. 



It is generally accepted that in butter the rancid flavor and 

 odor are due to the presence of the free fatty acids resulting from 

 hydrolysis, and it is well known that especially the volatile fatty 

 acids, such as butyric, etc., have a pungent odor that resembles 

 the rancid odor and flavor of butter. The free fatty acids re- 

 sulting from fat hydrolysis are expressed as, and determined by, 

 the acid value of the fat. The acid value would therefore ap- 

 pear to be a logical and correct measure of the degree of ran- 

 cidity of the butter. And in a great many cases rancid butter is 

 accompanied by a high acid value, as Jensen has shown. 



However, there is a vast volume of experimental data on 

 record which shows that quite often butter may have intense 

 rancidity while the acid value of the fat from this butter shows 

 no appreciable increase over the acid value in fat from the 

 same butter when fresh, and instances are also recorded where 

 a relatively high acid value was not accompanied by a pro- 

 nounced rancid character of the butter. In fact the fat of per- 

 fectly fresh butter shows a considerable acid value. 



It is therefore quite probable that even in the case of butter, 



1 Jensen Ueber das Ranzig-werden der Butter, Laridw. Jahrb. d. Schweiz. 

 1901. 



2 Kirchner Berichte d. deutsch. botan. Gesellschaft, 1888, p. 101. 



8 Le-wkowitsch Chemical Technology and Analysis of Oils, Fats and 

 Waxes, Vol. I ,p. 53 ,1914. 



